A 1998 study of 12 children suggested that their autism might be linked to measles vaccine -- given as part of the routine measles-mumps-rubella (MMR) childhood vaccine. The study's British authors suggested that some children may suffer unusually persistent infection with, or a harmful immune response to, the weakened live measles virus used in the vaccine.

In 2004, 10 of the study's 13 authors formally withdrew this hypothesis and rejected any link between MMR vaccination and autism or developmental disorders. By then, U.K. parents had become so worried by this theory that MMR vaccination rates plummeted from 94% to 80% of British children.

Two laboratories reported finding suspicious measles-virus genetic material associated with cases of autism. But two more recent studies found no such evidence; and the methods used in the earlier studies have been called into question. Now Gillian Baird, FRCPaed, of Guy's Hospital, London, and colleagues report data from a much larger study.

Baird and colleagues looked for measles virus and antibody responses to measles virus in U.K. children aged 10 to 12. The study included 98 children with autism, 52 children with special educational needs but not autism, and 90Â children without developmental problems.

"No association between measles vaccination and autism spectrum disorder was found," Baird and colleagues report in the Feb. 5 online issue of Archives of Disease in Childhood.

Some children with autism appear to be developing normally and then regress, losing communication skills they already had developed. This regression occurs at about the same time as children complete their childhood vaccinations. But in the Baird study, children with regressive autism had no unusual responses to measles vaccination.

Fortunately, the scare over MMR vaccine has not had a significant effect on U.S. children, says pediatrician Lance Rodewald, MD, director of the CDC's Immunization Services Division.

"Right now, coverage with measles vaccine and all other vaccines has never been higher," Rodewald tells WebMD. "We have not seen any decrease in measles vaccine coverage in the U.S. The coverage is 92.4% nationally in 19- to 35-month-olds."

As a result, there's been no spread of measles in the U.S. for the last decade.

"In other parts of the world, measles still rages on," Rodewald says. "That is one reason we want to maintain high coverage, because we don't want unprotected kids around when a case comes in. It is always just a plane ride away."